Telephone-exchange system



Feb. 1, 1927.

J. E. ROGERS TELEPHONE EXCHANGE SYSTEM Filed Aug. 26, 1924 Mymfar v (Mae i ffiayera Patented Feb. 1, 1927.

UNITED STATES rran'r orrica.

JOSEPH E. ROGERS, OF NEW YORK, N. Y., ASSIGNOIB. TD WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION 01 NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed August 26, 1924. Serial No. 734,153.

This invention relates to private branch exchangetelephone systems, and more par ticularly to two ,way tie lines for interconnecting two private branch exchange switchboards.

The object of the invention is to increase the operating efliciency of circuits of this character in their interconnection of a plurality of private branch exchanges, and to provide improved means for signaling and supervision thereover.

A feature of the invention is the circuit arrangement whereby an operator at either interconnected private branch exchange, may signal the distant operator by actuating the usual ringing key thereby connecting the usual low frequency ringing current to the tie line which serves to disconnect all bridged equipment at that end of the tie line, and to connect battery and ground to the tip and ringing conductors of the line to actuate apparatus and signal the operator at the distant end. 1

Another feature in connection therewith is a provision against false signaling in this manner that may be caused by capacity or inductive disturbances.

It is well known in the art that a great difliculty to be overcome in the use of alternating current for signaling purposes in systems of this character is the false signaling that often results from sudden and run expected discharges of condensers associated with a line and in the case of very long lines the condensers formed by the conductors of the line itself. Due to the use of alternating current for signaling, such condensers are charged and discharged in either direction due to the fact that at the cessation of the application of such current the applied potential may be. in either direction. As a result discharges may take place in either direction and are therefore beyond control. Thus false signaling often results with resultant losses in operating efficiency and service. By the use of direct current, however, the condensers are always charged in the same direction and consequently the direction of discharge is always known. In consequence. false sig naling is overcome while the advantage of signaling by means of the usual ringing key is retained.

Further, it has been found that due to the disconnection of all bridges at the signal ing end, by the use of this circuit arrangement, an appreciable increase in the length of the trunk loop that can be employed is attained, over the maximum trunkloop that heretofore could be satisfactorily used, under equal conditions.

Other features not specifically mentioned above, will more readily appear from the following description, in conjunction with the accompanying drawing in which a two way tie line embodying the invention is shown together with sufficient connecting apparatus to properly illustrate its features.

To refer to the drawing, A, and B represent two private branch exchanges interconnected by trunk L. Enclosure C represents that portion of the equipment identical to that shown at exchange A that is not shown at B. X represents one of the stations served by exchange A, and Y represents a station served by exchange B. It will be assumed that stations X and Y may be suitably connected with their respective private branch exchanges A. and B, and. therefore the portions of the line circuit not essential to a proper understanding of the invention have been omitted.

A detailed description of the operation of the circuit arrangement of the invention will now be given.

Let us assume that a station X of private branch exchange A desires to establish a connection with a station Y of exchange B.

Station X will in the usual manner signal the operator at exchange A, who will accordingly insert plug P ofthe trunk cord circuit into the outgoing trunk jack J associated with trunk L. Cord supervisory relay 11 will thereupon be actuated, pull over its armature and prevent the lighting of lamp 10, over a circuit including the tip and ring connections of plug P and jack J, conductors L, L and bridging resistance 12. Lamp 10 is, therefore, prevented from lighting for reasons hereinafter described. Upon the insertion of plug P into jack J relay 14 will operate. The operator at exchange A will then actuate ringing key 18. The operation of the ringing key will cause ringing relay 15 bridged across the line to operateover an obvious circuit. Relay 15 in operating will close its contacts 16 and cause relay 17 to be energized over the following circuit: grounded battery, relay 17, contacts 16 of relay 15 to ground 18. Relay 1'? will thus operate to close its contacts 19 and 20, and therefore by opening the tip and ring conductors L and L removes all bridges at exchange A from across the trunk L, over which is now closed a battery circuit as follows: grounded battery, front contact of relay 17, conductor 2 of trunk L, through the bridge at exchange B, conductor 1 of trunk L and ground on the make contact of relay 17 through contacts 19. The attendant at exchange B is thereby signaled in a manner fully explained hereinafter. Furthermore, when relay 17 is energized and the tip and ring conductors are opened to remove all bridges at exchange A, the normally closed circuit including relay 21, is opened.

Upon the release of ringing key 13 by the operator at exchange A relay 15 restores to normal, thereby releasing relay 17. Relay 17, in deenergizing. allows the tip and ring conductors L L to restore and close the trunk for talking purposes.

It may be observed therefore, that by the actuation of the usual ringing key by the operator at private branch exchange A, all bridges at this exchange were removed from across the trunk and a direct battery circuit closed over the trunk to signal the operator at the distant exchange B.

Similarly, if the operator at exchange B desired to signal exchange A, the actuation of ringing key 13 would serve to disconnect all bridges at that end of the line and close a similar battery circuit for signaling or supervising the other end.

Assuming now that station X is through talking with station Y, that the cord circuits at each end are still connected and that the operator at exchange B desires to signal exchange A and accordingly actuates ringing key 13. All bridges will now be removed at that end, B, and battery and ground will, in similar manner and as hereinbefore described, be placed on the line to now operate relay 21 at exchange A. Relay 21 in operating will then cause relay 22 to operate which will in turn result in the operation of relay 2?) over obvious circuits. The energization of relay 23 will open the circuit including impedance coil 12 at contacts 24 and thus release cord supervisory relay 11. The release of cord supervisory relay 11 will close contacts 25 and the circuit for cord signal lamp 10 from grounded battery, through the lamp, contacts 25, grounded sleeve of jack J to grounded armature of relay 14, this relay being operated as long as plug P remains in jack J. The lamp 10 will now light, to apprise the operator at exchange A that exchange B is signaling. The operator at exchange A will thereupon remove plug P from jack J, lamp 10 will be extinguished, and the circuit returned to normal. It should be noted that relay 22 is slow in operating. False signals, as when relay 21 operates from capacity or inductive charges or discharges will, therefore, be incapable of actuating relay 22 because of its sluggish action. Only the application of steady ringing current at the distant exchange will be sufiicient to enable its energization, and thus false operation thereof is effectively prevented.

If station Y now be considered to originate a call, the operator at exchange B will insert plug 1? into J, actuate ringing key 13 and cause battery and ground to be placed on the trunk to operate relay 21 as above described. The operation of relay 21 will cause the operation of relays 22 and 23 as hereinbefore described. Inasmuch as relay 14 is nonenergized relay 23 in operating will lock itself in a circuit from grounded battery of relay 23, through relay 23, contacts 26 and grounded armature of relay 14. Relay 23 in operating opens the circuit including impedance coil 12 across the tip and ring conductors L L of the line and also causes line lamp 27 to light in the following circuit: grounded battery, contacts 28, contacts 29, lamp 27 to ground. Incidentally ground 18 will be removed from the armature of relay 15.

Upon observing the illumination of lamp 27, the operator at exchan e A will now respond by inserting plug i? into jack J. Belay 14 will now operate, as hereinbefore described, and hence open the looking circuit for relay 23 which will now release. Lamp 27 will thereupon be extinguished through the opening of contacts 28; the circuit including bridging impedance 12 across the tip and ring of the line will again be closed at contacts 24, and the ground on the armature of relay 15 replaced. The ground on the armature of relay 15 was purposely removed to prevent a possible false operation of relay 17 which would otherwise take place if relay 15 falsely operated due to inductive char 'es or discharges after the insertion of plugi? into jack J. This effectively guards against closing the battery circuit for falsely signaling the calling operator of exchange 13.

lVith both operators now plugged in, supervision or signaling may be had by operation of the ringing key, as previously described. Again, as hereinbefore shown, upon the distant operator ringing ofi, the called end is signaled, and upon removing the trunk cord from the trunk jack, the circuit restores to normal.

Upon the seizure of a trunk, for example at exchange A by station X and the consequent operation of relay 14, busy signal 80 will be operated in series with the busy sig nals of the lines serving all other stations, for example that of the station associated with the multiple Z, that are served by the trunk, through a circuit including grounded battery, armature of relay 1%, contacts 31, busy signal and in series through the re maining busy signals, for example 32 of the multiple Z. The operation of relay 14 also serves to ground the sleeves of all the multiple trunk acks in an obvious circuit. The busy condition of the trunk L if in use by any station would therefore be made known to the operator. Upon the release of relay 14: at the termination of the call, the busy signals will return to normal and any other station be free to use the trunk, its nonbusy condition being clearly indicated.

\Vhat is claimed is:

1. In a private branch exchange telephone system, a two-Way trunk line said trunk line having an appreciable capacity effect between the conductors thereof, a plurality of bridges at each end of said trunk line, an operators position at each end thereof. a source of alternating current and a source of direct current at each of said positions, means at each end of said trunk line including a ringing key and said source of alternating current whereby the operator at one of said positions may remove the bridges thereat and connect the source of direct current to the said trunk to signal the operator at the other of said positions, said bridges acting thereafter to dissipate the charge left on the conductors of said trunk by the application of said direct current.

2. In a telephone system, a two-Way trunk circuit including a plurality of bridges at each end thereof, means including a ringing key to connect a current of a certain characteristic for disconnecting all bridges at one end thereof and cause the operation of a signal at the other end by a current of a different characteristic, capacity condensers in said'trunk adapted to charge and discharge in two directions, and means Whereby the actuation of said signal is responsive solely to the actuation of said ringing key and unresponsive to the operation of said condensers.

In Witness whereof I hereunto subscribe my name this 22nd day of August A. D.,

JOSEPH E. ROGERS. 

